The threat of a national fuel strike has receded after the Acas conciliation service confirmed that peace talks between tanker drivers and haulage companies will take place on Wednesday.

Acas announced the discussions after fuel distributors agreed an agenda for the talks, to be held at an undisclosed location. "We have now held briefings with all the relevant parties and can confirm that substantive conciliation talks will take place on Wednesday 4 April," Acas said.

The move pushes back the likely date for any strike well into next week, because seven days' notice must be given. Because 23 April is the date their mandate expires, the drivers must declare strike dates by 16 April.

Unite, the trade union representing the 2,000 drivers balloted for strike action last month, had submitted a nine-point outline for talks to Acas. Following Monday's announcement, it now appears that the seven haulage companies involved in the dispute have given their backing to the agenda drawn up by Acas. In keeping with Acas procedures, the Unite representatives and fuel distributors are expected to sit in separate rooms during the first phase of negotiations.

The news came as the petrol retailers' association, the RMI, wrote to the energy secretary, Ed Davey, to warn that "the UK's energy resilience for retail supply of road transport fuels is at a historically low level".

Government reassurance that there was "no urgency" for drivers to top up appeared to be undermined by the letter, which cited a poll of 5,500 independent petrol stations showing "at least" 30% of sites had run out of petrol, diesel or both.

Warning of a repeat of last week's fuel panic, the RMI chairman, Brian Madderson, said: "The government needs to understand that the panic buying witnessed last week will be instantly repeated should the supply-side logistics come under renewed threat. This is merely the consumer's self-preservation instinct as our society is completely structured around road transport, especially in rural areas."

The letter was published as a Department of Energy and Climate Change spokesman said filling stations were moving towards normal stock levels, with fewer stations running dry. He said there was "no urgency" to top up tanks with a strike over Easter having been ruled out. On suggestions that fuel shortages will continue through Easter, a spokesman said: "This doesn't reflect the whole picture. Suppliers are telling us that there is no shortage of supply, that forecourts are being restocked and are returning to normal levels."

A senior figure at Unite said tanker drivers' terms and conditions were being eroded by outsourcing of petrol deliveries. Speaking to ITV's Daybreak, the assistant general secretary of Unite, Diana Holland, said: "We want a negotiated settlement. That won't happen without all parties coming together.

"This industry used to be one run by the oil companies alone. Over the years it's been contracted out to other companies and the conditions and the terms were kept pretty solidly at the beginning. But over the years they have become eroded and eroded."

She added: "This is not a new issue. We have been alerting the government all the way along. The people that are on the best conditions, the best rates of pay and the best training – we want to keep that for them. We want to put a floor in, under which no one can fall. When the contract negotiations take place, we want the oil companies, the retailers, and the distribution companies to say no one will fall below this standard."